Phenytoin Flashcards
None linear kinetics is what
saturable meaning Cl and VD will change with doses and we cannot predicted half life
what is conatsnt in linear kinetics
AUC, Cmax and Css
Satuarble kinetics as concentration rises what happens to clearance?
Clinical indications of this?
- clearence decreases
- making it very difficult to use to interpret doses or uses intitae dose changes
what is mixed-order pharmacokinetics
displaying first first order at low concentrtaions then zero order kientics at high concentrations
at low concenrtaions what kinetics do you expect for mixed order
first order
at high concentrations what kinetics do you expect for mixed order
zero order
in non-linear kinetics if MD is increase what kind of effect do we expect in the plasma cocnentraion
since the Cl decreases with more drug we see a disproportional rise in plasma concentration
when do drugs swithc from first order to zero order kinetics in mixed?
EX: phenytoin and theophylline
depedn on drug
Phenytoin - at therpautic levels
Theophylline at toxic level
what models decribes saturable enxymes
michealis menton kinetics
based off M-M kinetics at low concentration of CSS increase in CSS cause what to happen to elimination
proprotional increase in elimination
based off M-M kinetics at very high concentration of CSS increase in CSS cause what to happen to elimination
very little change in elimination
in M-M kinetics what happens with increase of CSS?
as css increase the increase in elimination dampen
what is Vm mean
the maximum rate of elimiantion in a certain time
what is Km
drug concentration when elimination is working at half capacity (half max rate)
point above which drug stauartion is likely
called the Michaelis constant
KM and affinty
low km
high km
inverse relation
low km - high affinity
high km - low affinity
relationship bw cp, km, and vmax
if cp»>km
stauation condition
elimiantion rate is indepednt of Cp
relationship bw cp, km, and vmax
if cp«<km
non-stauaation kinetics
elimination is depedent on Cp
time to steady state linear kinetics
5-7 half lives
time to steady sate non-linear kinetics
we can’t use the half life rule so we look at time to 90% of CSS so t90
how to make a linear representative of non-linear kinetics
y-intercept = 1/vmax
slope = km/vmax
X intercepit = 1/km
x-axis in 1/css
y-axis is 1/dose (mg/day)
increase in km means what for affinty, realistically whats happening, and Cp
- less affinity
- with co-administration of competitive enzyme inhibitors
- at lower concentration less CP means rate of metabolism is less
at normal km then cp is higher
Decrease km
- higher affinity
- co-administration of other drugs that displace our drug from plasma proetisn
- relatively small Cp measure
increased vmax
- maxmate rate of enxymes molcules increAse for metabolism
- enzyme inducer
- reduced Cp across all ranges
decreased vmax
- decrease in enxymes for metabolism
- disease states
- increase plasma concatention
